Josef “Jeff” Sipek


This is a (long overdue) reply to Ilya’s post: SMPT – Time to chuck it.

I’m going to quote it here, and reply to everything in it. Whenever I say "you," I mean Ilya. So, with that said, let’s get started.

E-mail, in particular SMTP (Simple Mail Transfer Protocol) has become an integral part of our lives, people routinely rely on it to send files, and messages. At the inception of SMTP the Internet was only accessible to a relatively small, close nit community; and as a result the architects of SMTP did not envision problems such as SPAM and sender-spoofing. Today, as the Internet has become more accessible, scrupulous people are making use of flaws in SMTP for their profit at the expense of the average Internet user.

Alright, this is pretty much the only thing I agree with.

There have been several attempts to bring this ancient protocol in-line with the current society but the problem of spam keeps creeping in. At first people had implemented simple filters to get rid of SPAM but as the sheer volume of SPAM increased mere filtering became impractical, and so we saw the advent of adaptive SPAM filters which automatically learned to identify and differentiate legitimate email from SPAM. Soon enough the spammers caught on and started embedding their ads into images where they could not be easily parsed by spam filters.

A history lesson…still fine.

AOL (America On Line) flirted with other ideas to control spam, imposing email tax on all email which would be delivered to its user. It seems like such a system might work but it stands in the way of the open principles which have been so important to the flourishing of the internet.

AOL (I believe Microsoft had a similar idea) really managed to think of something truly repulsive. The postal system in the USA didn’t always work the way it does today. A long time ago, the recipient paid for the delivery. AOL’s idea seems a lot like that.

There are two apparent problems at the root of the SMTP protocol which allow for easy manipulation: lack of authentication and sender validation, and lack of user interaction. It would not be difficult to design a more flexible protocol which would allow for us to enjoy the functionality that we are familiar with all the while address some, if not all of the problems within SMTP.

To allow for greater flexibility in the protocol, it would first be broken from a server-server model into a client-server model.

This is first point I 100% disagree with…

That is, traditionally when one would send mail, it would be sent to a local SMTP server which would then relay the message onto the next server until the email reached its destination. This approach allowed for email caching and delayed-send (when a (receiving) mail server was off-line for hours (or even days) on end, messages could still trickle through as the sending server would try to periodically resend the messages.) Todays mail servers have very high up times and many are redundant so caching email for delayed delivery is not very important.

"Delayed delivery is not very important"?! What? What happened to the whole "better late than never" idiom?

It is not just about uptime of the server. There are other variables one must consider when thinking about the whole system of delivering email. Here’s a short list; I’m sure I’m forgetting something:

  • server uptime
  • server reliability
  • network connection (all the routers between the server and the "source") uptime
  • network connection reliability

It does little to no good if the network connection is flakey. Ilya is arguing that that’s rarely the case, and while I must agree that it isn’t as bad as it used to be back in the 80’s, I also know from experience that networks are very fragile and it doesn’t take much to break them.

A couple of times over the past few years, I noticed that my ISP’s routing tables got screwed up. Within two hours of such a screwup, things returned to normal, but that’s 2 hours of "downtime."

Another instance of a network going haywire: one day, at Stony Brook University, the internet connection stopped working. Apparently, a compromised machine on the university campus caused a campus edge device to become overwhelmed. This eventually lead to a complete failure of the device. It took almost a day until the compromised machine got disconnected, the failed device reset, and the backlog of all the traffic on both sides of the router settled down.

Failures happen. Network failures happen frequently. More frequently that I would like them to, more frequently than the network admins would like them to. Failures happen near the user, far away from the user. One can hope that dynamic routing tables keep the internet as a whole functioning, but even those can fail. Want an example? Sure. Not that long ago, the well know video repository YouTube disappeared off the face of the Earth…well, to some degree. As this RIPE NCC RIS case study shows, on February 24, 2008, Pakistan Telecom decided to announce BGP routes for YouTube’s IP range. The result was, that if you tried to access any of YouTube’s servers on the subnet, your packets were directed to Pakistan. For about an hour and twenty minutes that was the case. Then YouTube started announcing more granular subnets, diverting some of the traffic back to itself. Eleven minutes later, YouTube announced even more granular subnets, diverting large bulk of the traffic back to itself. Few dozen minutes later, PCCW Global (Pakistan Telecom’s provider responsible for forwarding the "offending" BGP announcements to the rest of the world) stopped forwarding the incorrect routing information.

So, networks are fragile, which is why having an email transfer protocol that allows for retransmission a good idea.

Instead, having direct communication between the sender-client and the receiver-server has many advantages: opens up the possibility for CAPTCHA systems, makes the send-portion of the protocol easier to upgrade, and allows for new functionality in the protocol.

Wow. So much to disagree with!

  • CAPTCHA doesn’t work
  • What about mailing lists? How does the mailing list server answer the CAPTCHAs?
  • How does eliminating server-to-server communication make the protocol easier to upgrade?
  • New functionality is a nice thing in theory, but what do you want from your mail transfer protocol? I, personally, want it to transfer my email between where I send it from and where it is supposed to be delivered to.
  • If anything eliminating the server-to-server communication would cause the MUAs to be "in charge" of the protocols. This means that at first there would be many competing protocols, until one takes over - not necessarily the better one (Betamax vs. VHS comes to mind).
  • What happens in the case of overzealous firewall admins? What if I really want to send email to, but the firewall (for whatever reason) is blocking all traffic to

Spam is driven by profit, the spammers make use of the fact that it is cheap to send email. Even the smallest returns on spam amount to good money. By making it more expensive to send spam, it would be phased out as the returns become negative. Charging money like AOL tried, would work; but it is not a good approach, not only does it not allow for senders anonymity but also it rewards mail-administrators for doing a bad job (the more spam we deliver the more money we make).

Yes, it is unfortunately true, money complicates things. Money tends to be the reason why superior design fails to take hold, and instead something inferior wins - think Betamax vs. VHS. This is why I think something similar would happen with competing mail transfer protocols - the one with most corporate backing would win, not the one that’s best for people.

Another approach is to make the sender interact with the recipient mail server by some kind of challenge authentication which is hard to compute for a machine but easy for a human, a Turing test. For example the recipient can ask the senders client to verify what is written on an obfuscated image (CAPTCHA) or what is being said on a audio clip, or both so as to minimize the effect on people with handicaps.

Nice thought about the handicapped, but you are forgetting that only 800-900 million people speak English (see Wikipedia article: Wikipedia). That is something on the order of 13-15 percent. Sorry, but "listening comprehension" tests are simply not viable.

Obfuscated image Wikipedia article: CAPTCHAs are "less" of a problem, but then again, one should consider the blind. I am not blind, and as a matter of fact my vision is still rather good (even after years of staring at computer screens), but at times I’m not sure what those "distorted text" CAPTCHAs are even displaying. I can’t even begin to imagine what it must be like for anyone with poor vision.

You seem to be making the assumption that most if not all legitimate email comes from humans. While that may be true for your average home user, let’s not forget that email is used by more technical people as well. These people will, and do, use email in creative ways. For example, take me…I receive lots of emails that are generated by all sorts of scripts that I wrote over time. These emails give me status of a number of systems I care about, and reminders about upcoming events. All in all, you could say that I live inside email. You can’t do a CAPTCHA for the process sending the automated email (there’s no human sending it), and if you do the CAPTCHA for the receiving, you’re just adding a "click here to display the message" wart to the mail client software user interface.

Just keep in mind that all those automated emails you get from "root" or even yourself were sent without a human answering a CAPTCHA.

It would be essential to also white list senders so that they do not have to preform a user-interactive challenge to send the email, such that mail from legitimate automated mass senders would get through (and for that current implementation of sieve scripts could be used). In this system, if users were to make wide use of filters, we would soon see a problem. If nearly everyone has a white list entry for Bank Of America what is to prevent a spammer to try to impersonate that bank?

White listing is really annoying, and as you point out, it doesn’t work.

And so this brings us to the next point, authentication, how do you know that the email actually did, originate from the sender. This is one of the largest problems with SMTP as it is so easy to fake ones outgoing email address. The white list has to rely on a verifiable and consistent flag in the email. A sample implementation of such a control could work similar to the current hack to the email system, SPF, in which a special entry is made in the DNS entry which says where the mail can originate from. While this approach is quite effective in a sever-server architecture it would not work in a client-server architecture. Part of the protocol could require the sending client to send a cryptographic-hash of the email to his own receiving mail server, so that the receiving party’s mail server could verify the authenticity of the source of the email. In essence this creates a 3 way handshake between the senders client, the senders (receiving) mail server and the receiver’s mail server.

I tend to stay away from making custom authentication protocols.

In this scheme, what guarantees you that the client and his "home server" aren’t both trying to convince the receiving server that the email is really from whom they say it is? In kerberos, you have a key for each system, and a password for each user. The kerberos server knows it all, and this central authority is why things work. With SSL certificates, you rely on the strength of the crypto used, as well as blind faith in the certificate authority.

At first it might seem that this process uses up more bandwidth and increases the delay of sending mail but one has to remember that in usual configuration of sending email using IMAP or POP for mail storage one undergoes a similar process,

Umm…while possible, I believe that very very large majority of email is sent via SMTP (and I’m not even counting all the spam).

first email is sent for storage (over IMAP or POP) to the senders mail server and then it is sent over SMTP to the senders email for redirection to the receivers mail server. It is even feasible to implement hooks in the IMAP and POP stacks to talk to the mail sending daemon directly eliminating an additional socket connection by the client.

Why would you want to stick with IMAP and POP? They do share certain ideas with SMTP.

For legitimate mass mail this process would not encumber the sending procedure as for this case the sending server would be located on the same machine as the senders receiving mail server (which would store the hash for authentication), and they could even be streamlined into one monolithic process.

Not necessarily. There are entire businesses that specialize in mailing list maintenance. You pay them, and they give you an account with software that maintains your mailing list. Actually, it’s amusing how similar it is to what spammers do. The major difference is that in the legitimate case, the customer supplies their own list of email address to mail. Anyway, my point is, in these cases (and they are more common than you think) the mailing sender is on a different computer than the "from" domain’s MX record.

Some might argue that phasing out SMTP is a extremely radical idea, it has been an essential part of the internet for 25 years.

Radical? Sure. But my problem is that there is no replacement. All the ideas you have listed have multiple problems - all of which have been identified by others. And so here we are, no closer to the solution.

But then, when is the right time to phase out this archaic and obsolete protocol, or do we commit to use it for the foreseeable future. Then longer we wait to try to phase it out the longer it will take to adopt something new. This protocol should be designed with a way to coexist with SMTP to get over the adoption curve, id est, make it possible for client to check for recipients functionality, if it can accept email by this new protocol then send it by it rather than SMTP.

Sounds great! What is this protocol that would replace SMTP? Oh, right there isn’t one.

The implementation of such a protocol would take very little time, the biggest problem would be with adoption.

Sad, but true.

The best approach for this problem is to entice several large mail providers (such as Gmail or Yahoo) to switch over. Since these providers handle a large fraction of all mail the smaller guys (like myself) would have to follow suit.

You mentioned Gmail…well, last I heard, Gmail’s servers were acting as open proxies. Congratulations! One of your example "if they switch things will be better" email providers is allowing the current spam problem to go on. I guess that makes you right. If Gmail were to use a protocol that didn’t allow for spam to exist, then things would be better.

There is even an incentive for mail providers to re-implement mail protocol, it would save them many CPU-cycles since Bayesian-spam-filters would no longer be that important.

What about generating all those CAPTCHAs you suggested? What about hashing all those emails? Neither activity is free.

By creating this new protocol we would dramatically improve an end users experience online, as there would be fewer annoyances to deal with. Hopefully alleviation of these annoyances will bring faster adoption of the protocol.

I really can’t help but read that as "If we use this magical protocol that will make things better, things will get better!" Sorry, but unless I see some protocol which would be a good candidate, I will remain sceptical.

As a side note, over the past  90 days, I received about 164MB of spam that SpamAssassin caught and procmail promptly shoved into the spam mail box. Do I care? Not enough to jump on the "let’s reinvent the email system" bandwagon. Sure, it eats up some of my servers clock cycles, and some bandwidth, the spam that gets to me is the few pieces that manage to get through, and show up in my inbox. Would I be happy if I didn’t have to use a spam filter, and not have to delete the few random spams by hand? Sure, but at least for the moment, I don’t see a viable alternative.


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